1. Field of the Invention
The invention relates to a key telephone unit and a key telephone system, and more particularly to a key telephone unit and a key telephone system both including a telephone.
2. Description of the Related Art
A conventional key telephone system is comprised generally of a telephone including selection buttons which emit a light to thereby inform a user of a public switched line through which a call is made, a key telephone unit which controls a telephone in transmitting a call and receiving a call, and a public switched line connected between the key telephone unit and a central telephone exchange.
In such a conventional key telephone system as mentioned above, a selection button associated to a busy public switched line is controlled to emit a light for a user to recognize that the line is now busy, and facilitate a user to push a selection button associated to a non-busy public communication line. Thus, a user can select a particular public communication line among a plurality of public communication lines, and establish connection line between his/her telephone and a public communication line.
When a call is made to the key telephone system through a public switched line, a user can connect his/her telephone to the public switched line by pushing a selection button associated with the public switched line through which the call is made.
A telephone line connecting a telephone and a key telephone unit to each other in a key telephone system causes noises, if a signal to be transmitted to a telephone from a key telephone unit for turning a selection button on is combined into a communication signal. Hence, a key telephone system is generally designed to include further two lines through which the above-mentioned signal for turning a selection button on is transmitted or received, as well as two telephone lines necessary for making communication therethrough. That is, a key telephone system is usually designed to include four telephone lines.
Hereinbelow is explained a conventional key telephone system having four telephone lines, with reference to FIG. 1.
A conventional key telephone system illustrated in FIG. 1 is comprised of telephones E1 to En, a key telephone unit 2, telephone lines F1 to Fn connecting the telephones E1 to En and the key telephone unit 2 to each other, and public switched lines B1 to Bn connected to the key telephone unit 2.
Each of the telephones E1 to En is designed to have selection buttons (not illustrated), a communication interface 8 and a communication controller 7. Herein, the selection buttons correspond to the public switched lines B1 to Bn. A particular public switched line is selected by pushing a selection button associated with the particular public switched line.
Each of the telephone lines F1 to Fn is comprised of four lines including two lines necessary for making communication therethrough and two lines necessary for transmitting and receiving signals therethrough such a signal for turning a selection button on.
The communication interface 8 in the telephone E1, for instance, allows a user to make communication with the other telephones E2 to En, and allows the telephone E1 to connect to the public switched lines B1 to Bn.
The communication controller 7 transmits a loop signal and a light-on signal to the key telephone unit 2, and receives a button-on signal from the key telephone signal 2. The loop signal indicates that a telephone associated with the communication controller 7 is hooked off, and the light-on signal indicated that a particular selection button among the selection buttons was pushed. The button-on signal indicates a particular selection button to be turned on.
The key telephone unit 2 is comprised of first ports C1 to Cn, second ports D1 to Dn, a switch 3, and a controller 4.
Each of the first ports C1 to Cn connects the associated telephone E1 to En to the switch 3. On receipt of a loop signal, each of the first ports C1 to Cn transfers the received loop signal to the controller 4 for informing the controller 4 of which telephone among the telephones E1 to En is hooked off.
Each of the second ports D1 to Dn connects the associated public switched line B1 to Bn to the switch 3. On detecting a call transmitted through the public switched lines B1 to Bn, each of the public switched lines B1 to Bn informs the controller 4 of the detection.
The switch 3 connects the public switched lines B1 to Bn to telephones E1 to En to each other, or connects the telephones E1 to En to each other.
When a call is made through any one of the public switched lines B1 to Bn, the controller 4 identifies one of the public switched lines B1 to Bn through which a call is made, based on signals transmitted from the second ports D1 to Dn, and produces a light-on signal in association with the public switched line B1 to Bn through which a call was made. The thus produced light-on signal is transmitted to the associated telephone E1 to En for turning a selection button thereof on.
When a call is made from the telephone E1, for instance, through the public switched line B1, the controller 4 identifies the telephone E1, based on both a button-on signal indicating that the selection button associated with the public switched line B1 is pushed and emits a light, and a loop signal received from the first port C1, and transmits a light-on signal associated with the public switched line B1 selected by the telephone E1, to the telephones E1 to En.
The controller 4 further transmits a command signal to the switch 3. In accordance with the command signal, the switch 3 connects any one of the public switched lines B1 to Bn to any one of the telephones E1 to En, or connects any two of the telephones E1 to En to each other.
Hereinbelow is explained an operation of the conventional key telephone system illustrated in FIG. 1.
It is now assumed that the telephone E1 transmits a call. If the telephone E1 is hooked off, the communication controller 7 associated with the telephone E1 transmits a loop signal to the first port C1. If a user of the telephone E1 does not select a particular public switched line among the public switched lines B1 to Bn by pushing a selection button associated with a particular public switched line, but wants to use any one of the public switched lines B1 to Bn, the controller 4 in the key telephone unit 2 detects non-used or available public switched lines B1 to Bn, and transmits a command to the switch 3 for causing the switch 3 to connect the public switched line B1 to the hooked-off telephone E1.
Then, the controller 4 transmits an instruction to the switch 3 to transmit the loop signal having been received from the telephone E1 to the public switched line B1 through the second port D1.
Then, the switch 3 connects the first port C1 having been connected to the telephone E1, to the second port D1 having been connected to the public switched line B1, to thereby connect the telephone E1 and the public switched line B1 to each other.
Herein, it is assumed that a call is made to the key telephone unit 2 through the public switched line B1.
A call signal transmitted from an exchange (not illustrated) is introduced into the key telephone unit 2 through the public switched line B1 to which the exchange is connected.
Then, the second port D1 in the key telephone unit 2 detects the call signal transmitted through the public switched line B1, and informs the controller 4 of the detection of the call signal.
The controller 4 informed of the detection of the call signal identifies the public switched line B1 through which the call signal was transmitted, and produces a light-on signal associated with the public switched line B1. The thus produces light-on signal is transmitted to the telephones E1 to En.
On receipt of the light-on signal through the communication controller 7, each of the telephones E1 to En turns on a selection button indicated by the received light-on signal for annunciating a user that a call has been received.
Then, a user selects and pushes a particular selection button of the telephone E1 and hook the telephone E1 off. As a result, the communication controller 7 of the telephone E1 transmits a loop signal and a button-on signal to the first port C1. As mentioned earlier, a loop signal is produced when a telephone is hooked off, and a button-on signal is produced when any one of the selection buttons is pushed.
Then, when the first port C1 receives both the loop signal and the button-on signal, the first port C1 informs the controller 4 that a particular telephone is hooked off, and a particular selection button is pushed.
Then, the controller 4 operates the switch 3 such that the telephone E1 having received the light-on signal and the loop signal and the public switched line B1 are connected to each other. Thus, a communication line is established between the telephone E1 and the public switched line B1.
The above-mentioned conventional key telephone unit and key telephone system did not have uniformity in specification. That is, there were various key telephone units and key telephone systems having different specification. Hence, it was necessary to purchase telephones inherent to selected key telephone unit and key telephone system. Such telephones are more expensive than generally available telephones.
In addition, such telephones are necessary to include an additional unit for conducting modular jack junction through a modem to be used for carrying out dial-up Internet connection.
Japanese Unexamined Patent Publication No. 58-137389 (A) has suggested an electronic key telephone unit including a plurality of button-type telephones, and a main unit having a switch network connecting a plurality of extension telephone circuits to the button-type telephones, and a central processing unit which controls the switch network. The electronic key telephone unit further includes a memory circuit electrically connected to the central processing unit, and storing extension numbers of first and second button-type telephones when the first button-type telephone makes a call to the second button-type telephone to thereby connect the first and second button-type telephones to each other, and a display unit equipped in each of the button-type telephones. When the first button-type telephone makes a call to the second button-type telephone, if the second button-type telephone is busy or does not make a response, extension numbers of the first and second button-type telephones are stored in the memory circuit by operating buttons in the first button-type telephone, and the extension number of the first button-type telephone is displayed in the display unit of the second button-type telephone.
Japanese Unexamined Patent Publication No. 61-269492 (A) has suggested a key telephone system including a key telephone having a selector which selects a pair among a plurality of pairs of subscriber lines, a parent station, and a child station. The parent station includes first unit for detecting and analyzing a code for calling a person, input by a caller of the subscriber line at touch tone, and a first radio unit which selects a child station associated with the code, and transmits a selection number associated with the subscriber line. The child station includes a second radio unit which receives a radio signal transmitted from the first radio unit, and a display unit which reproduces voices in accordance with signals output from the second radio unit, and displays the selection number.
Japanese Unexamined Patent Publication No. 62-234454 (A) has suggested a line interface unit including a plurality of connection terminals for connecting a plurality of telephone type terminals including a telephone which automatically or manually transmits or receives a call, to at least one non-telephone type terminal, a terminal interface which controls interfaces between the telephone type terminals and the non-telephone type terminal, a connection terminal connected to a telephone line network, a second interface which controls an interface between the connection terminal and the telephone line network, a modem which modulates and demodulates data transmitted between non-telephone type terminals, a controller which controls operation of the above-mentioned parts. The controller cooperates with the parts to preferentially allow communication to be made, regardless that a call is transmitted or received.
Japanese Unexamined Patent Publication No. 1-208065 (A) has suggested a key telephone connected to an exchange system in which a number of a caller is annunciated to a receiver when the receiver receives a call made from the caller. The key telephone includes a subscriber interface connected to a digital subscriber line, a digital switch, a controller which controls operation of the subscriber interface and the digital switch, and a memory electrically connected to the controller. Data indicative of relation between an extension number and a caller's number, and data indicative of relation between an extension number and a station number included in a caller's number are stored in advance in the memory. The subscriber interface receives a caller's number, and the controller analyzes the received caller's number and makes comparison of the caller's number with data stored in the memory. The controller calls a telephone associated with the extension number in accordance with the stored data.
Japanese Unexamined Patent Publication No. 2000-151808 (A) has suggested an apparatus which receives a request from a subscriber, and connects the subscriber to Internet through a provider. The apparatus includes a subscriber line interface which receives a request to connect to Internet, from a subscriber, a first detector which detects the request, a second detector which detects a telephone number of the subscriber, based on the request, a time administrator which judges whether a time period during which the request has been received is within a time period allowable for providing Internet connection service, a first controller which makes inspection as to whether the telephone number of the subscriber is allowed to receive Internet connection service, a second controller which judges whether a response is made to the request, based on the inspection result, and an interface connected to the provider. The apparatus is accommodated in an exchange as an extension terminal.
However, the above-mentioned problems remain unsolved even in the above-mentioned Publications.